Pro. K- Beat Game and Save. You Might need earplugs the way he keeps shouting "JET GRIND RADIO!!" everytime he jumps.
Love Shockers- Get Jets on all Shibuya-Cho Missions(this includes Jet Crush, Grafitti, and Technique.).
Poison Jam-Get Jets on all Kogane-Cho Missions( once again, this includes Jet Tech, Crush, and Grafittis
Noise Tanks-Get Jets on all Benten-Cho Missions(I think you get the idea)
These are the minimum times you have to have left on the Jet Crush Missions to get Jets.
Kogane-I'm guessing 30 sec cause I get times like 25 and 26 and get Nitros.
To play as Poison Jam you must successfully complete with a Jet rank the Kogane-Cho levels.